The concept of respiratory therapy is well known in the art field, and a wide variety of respiratory diseases are treated by use of a positive pressure respiratory system. The positive pressure incident to such systems is generated by devices commonly referred to as ventilators, respirators or other such positive pressure machines. Generally, the concept is to provide a breathable gas mixture under pressure to the patient to facilitate the respiratory cycle of the patient.
Usually, such breathable gases consist of a composition of air and oxygen which is delivered to the patient under controlled conditions of pressure, temperature, water content and gas composition.
In the typical system, the gas is conducted from the ventilator to the patient by means of a tubing conduit, generally consisting of an inhalation tube and exhaled gases exhausted through an exhalation tube. Furthermore, it is generally accepted that in such systems, the inhalation and exhalation tubes respectively, are separate tubes separately interconnecting the ventilator with the patient face mask in order to complete the circuit as between the ventilator and the patient. The differences existing between the variety of systems available generally involve mainly materials of construction rather than in the make-up of the system. The tubing conduit is usually formed of a flexible material, which is chemically inert and fabricated into a cylindrical configuration, whether corrugated or otherwise, and reinforced in order to prevent kinking and collapse. The tubes or conduits are interconnected to the ventilator and to the patient by any suitable devices, although usually slip-type friction fittings are employed especially for pg,4 connection of the ventilator to the valving mechanism which is external to the patient. In addition, many of the current respiratory breathing circuits also incorporate a gas powered nebulizer, usually mounted to the housing of the valving mechanism, the nebulizer functioning to create a mist of a variety of liquid medications, which are then administered in conjunction with the positive gas pressure introduced through the inhalation tube.
Another feature of a respiratory circuit and system includes the provision of a heated humidifier which is interposed in the circuit between the ventilator and the inhalation tube. The purpose of the heated humidifier is to raise the temperature of the gas as well as to humidify the same prior to inhalation by the patient. In the usual system, the heater raises the liquid temperature to approximately 120.degree.-140.degree. F. which results in a gas temperature of approximately 110.degree.-130.degree. F. upon exit from the nebulizer or humidifer.
Insofar as the presently existing systems are concerned, a variety of problems have been encountered and it is the purpose of the present invention to overcome these difficulties which are inherent in the present systems. For example, the valving mechanism incident to systems presently available are generally extraneous to the system and the circuit, and hence, a great deal of dead space is usually present in the system. The dead space results in the patient generally breathing in previously exhaled gases during the inhalation cycle since any gas existing in the dead space will tend to be drawn back into the patient during the inhalation cycle. In the event that any bacterial growth develops in the dead space, it is obvious that the patient is exposed to the danger of inhaling contaminated gas.
In addition, CO.sub.2 is a respiratory stimulant and can cause hyper-ventilation with attendant unfavorable complications. Hence, it is deemed desirable not only to have the valving mechanism associated with the circuit per se, but also to position the valving mechanism closely adjacent to the patient to minimize the dead space.
Insofar as humidification and heating is concerned, it has been found that since the humidifier is generally positioned in the circuit in a position removed from the patient, that even though the gas may be heated and humidified, the gas will give off both heat and humidity as it travels through the tubing to the patient. For example, when the heat-saturated gas leaves the humidifier through the tubing circuit, it will release heat by contact with the thin wall of the tubing conduit, which in turn is exposed to room air temperature, i.e. 70.degree.-75' F. Hence, it is frequently found that the inlet gas temperature just prior to entering the patient is approximately 85.degree. F. thereby accounting for a temperature drop of approximately 25.degree. F or more. As a result of the heat given up by the gas, condensation will occur in the tubing circuit resulting in a pool of liquid collecting in the tubing. It is apparent that the pooling of liquid in the tubing circuit is not desirable since such pooling actually reduces the lumen opening of the tubing at the point of pooling, which in turn may cause premature cycling of a pressure-cycled ventilator, since the reduced lumen presents a pressure gradient which the ventilator senses as a pressure increase. If the pressure equals the shut-off pressure of the ventilator, the ventilator will cycle off and the patient will not have received the proper pressure from the ventilator system. In a volume-cycled ventilator, the reduction in lumen at the point of pooling reduces the volume of gas delivered to the patient since the gas between the ventilator and the pool is compressed and hence, the patient does not receive the proper volume of gas. Furthermore, the compression of the gas is reflected in tubing compliance, or the distention of the tubing as a result of internal pressure and is an important factor in determining the setting of volume-cycled ventilators and is generally compensated for in making the initial settings of the ventilators. The change in volume produced by pooling, however, is not predictable and consequently, cannot be compensated for in the ventilator setting. In presently existing systems, this situation is compensated for by draining the tubing at frequent intervals in order to relieve the pooling problems. It is hence deemed desirable to reduce the amount of condensation in the tubing and one of the purposes of the present invention is to greatly reduce this problem.
Another problem incident to the heat loss of the gases as they travel through the tubing conduit from the humidifier to the patient is that if the temperature of the inhaled gas is below body temperature, there is a tendency of the body of the patient to give up heat to the gas. The heat given up by the patient is energy released as a result of the work by the patient's metabolic system and the continued demand for heat release requires the metabolic system to work harder and this work can become a significant factor in treating a critically ill patient. Additionally, as the temperature of the inhaled gas is raised, through heat loss by the patient, its relative humidity decreases. A humidity deficit in the gas is then created and since the gas can carry additional moisture as water vapor, the tendency is for the mucosal membranes in the respiratory system of the patient's body to give up water until the inhaled gas is saturated. This surrender of water vapor from the patient's mucosal membranes can cause complications since the mucous on those membranes will become drier and more viscous, making it more difficult to remove by cillial action. The accumulation of mucous inhibits adequate ventilation and can cause alveolar collapse infection, changes in blood gas levels, and other complications of a serious nature.
The present systems have attempted to alleviate this problem by increasing the moisture and temperature of the gas upon leaving the humidifier. However, it is apparent that where the gas is heated above body temperature in order to ensure a temperature close to body temperature upon delivery to the patient, the gas will pick up additional quantities of moisture in the humidifier and will lose the same through "rain out" during its travel through the tubing conduit. Hence, more frequent draining of the tubing conduit has been necessary where humidification is employed.
It is therefore deemed desirable to minimize the amount of extra heat generated in the humidifier while at the same time preventing and retarding heat loss in the tubing conduit since one is thereby more assured of the proper humidity and temperature level of the gas upon inhalation by the patient. It is another feature of this invention to provide a system which accomplishes this end.
Another difficulty which has been inherent in presently available systems relates to the nebulizer utilized to introduce atomized medications into the inhalation line. Present systems generally require that an operator manually fill the nebulizer prior to the respiratory therapy for the patient, and this operation is both time consuming and subject to human error. Furthermore, additional problems with sterility are introduced when an operator handles the nebulizer, especially where the nebulizer is intended to be in fluid communication with the tubing circuit for delivery of medicinal fluids to the patient. While the present nebulizers are relatively effective in creating atomization of the medicinal liquids therein, such nebulizers are affected in different degrees by the position of the nebulizer assembly with respect to the vertical-horizontal axis. For example, if the bottom of the capillary tube within the nebulizer is improperly positioned within the housing, no liquid will be aspirated in the capillary tubing. The present invention overcomes this difficulty by providing an improved and more simplified nebulizer including a capillary tube system which is designed to flotate on the surface of the medicinal fluid contained in the nebulizer and ensure that atomization of the medicinal fluid therein will occur during the inhalation therapy.